Particulate erosion of NiO scales

• Published in: Wear 1981-05, Vol.68 (3), p.305-331
• Main Authors: Zambelli, G., Levy, A.V.
• Format: Article
• Language: English
• ISSN: 0043-1648; 1873-2577
• DOI: 10.1016/0043-1648(81)90179-4

The erosion behavior of brittle oxide scales on ductile alloy substrates is not well known. The oxidation of commercially pure nickel in an air furnace at 1000°C produces relatively thick NiO scales which provide a base for an investigation of the erosion behavior of scales of more complex alloys. The NiO scales formed consisted of two distinct layers, a columnar outer layer and a fine-grained porous inner layer. The erosion testing was conducted at room temperature using an air blast tester. Angular SiC particles were used at velocities V p of 100 and 30 m s −1, and at impingement angles α of 20° and 90°. Erosion damage of the NiO scales was observed and interpreted using simplified postulates based on fracture propagation concepts. The NiO duplex scale is removed in a two-step mechanism. Plastic flow indentation and lateral crack growth in the columnar outer layer is the first step in the erosion mechanism. In the second step, pits are produced from hertzian cone fractures formed in the inner layer. The oxide is removed by the chipping away of the cracked scale of the outer and inner layers, which enlarges the pits. At greater velocities, particle sizes and impingement angles the erosion of the thinner oxide scales to the bare nickel occurred in times of the order of seconds. It was observed that the strengths of the bonds between the two scale layers and between the scale and the metal substrate were directly related to the erosion behavior. NiO scales thicker than 50μm introduced some protection during the initial period of erosion of the outer scale. The microstructure, mechanical properties and bonding state of the oxide layers are important parameters in the erosion behavior of oxide scales.